emit chimeric stats on PE

[Psy-Fer]

fix: count PE chimeric reads in Log.final.out

Summary

Log.final.out's "Number of chimeric reads" was always 0 for paired-end runs regardless
of --chimSegmentMin, because stats.record_chimeric() was never called in the PE
alignment loop.

The SE path correctly calls it whenever chimeric alignments are found. The PE path
collected and wrote chimeric output (junction file, WithinBAM supplementary records) but
skipped the stats call entirely.

Change

src/lib.rs — three lines added after the PE stats block, mirroring the SE pattern:

if params.chim_segment_min > 0 && !pe_chimeric.is_empty() {
    stats.record_chimeric();
}

pe_chimeric is the Vec<ChimericAlignment> returned from align_paired_read. It is
checked before the move into AlignmentBatchResults so no clone is needed.

Test plan

• cargo test — 434 tests passing, 0 failures
• cargo clippy --all-targets — 0 warnings
• cargo fmt --check — clean
• SE/PE benchmarks unchanged: SE 8604/8926 (96.4%), PE 8390/8390 both-mapped